1. Field of the Invention
This invention is in the field of continuous reduction of iron oxides which involves passing a particulate mixture of such oxides with a carbonaceous reducing agent through a conduit which is disposed in the path of hot flue gases for a time and at a temperature sufficient to cause reduction of the iron oxides to a form in which they can be conveniently used as a charge, for example, to an electric furnace.
2. Description of the Prior Art
The present invention has particular applicability to the economic reduction of mill scale to form a commercially usable product. Scale is a coating of oxide formed at high temperatures during rolling or forging operations. The scale varies according to the composition of the steel, the time and temperature of exposure to the oxidizing atmosphere, the nature and constancy of the atmosphere, and the manner of rolling. High pressure, for example, serves to embed the scale into the surface of the steel. When plain carbon steel is heated in an oxidizing atmosphere, the scale is made up of three layers. The layer next to the steel is FeO or a mixture of Fe and Fe.sub.3 O.sub.4. The outer layer is composed of Fe.sub.2 O.sub.3 and the middle layer which is the thickest layer consists of Fe.sub.3 O.sub.4.
This scale has presented a disposal problem in steel plants for many years. In plants having an integrated operation, the scale could be disposed of by using it as a charge in a blast furnace. In the absence of a blast furnace, however, the steel producer usually had to collect the mill scale and sell it to persons who could use it as a low grade source of iron. The temperatures involved and the cost of the reducing agent make hydrogen reduction of mill scale a nonfeasible process commercially.